Best, I honestly dont think you can go that way. Play what you enjoy the most. There are no best
You asking about pvp in the dopic but then talk about dps in the post, dps is PVE related.
My opinion Pvp
Pally, fun, easy. But as you run into more skilled players it gets harder
(I have a pally)
Druid, feral is fun in pvp, but def not op. Balance most say sux. Resto your best option
(Druid is my main, pve mostly but some pvp)
Warrior, are doing allot better these days. Well thats what my 2k rated friend says. And he luves his warrior.
Mage is really really not easy imo, but loads of fun and rewarding. Luv pvping with my mage and only class that annoys me is rogues really.
As I said above its all about what you enjoy playing. Every class basically has its anti-class and the difficulty of classes obviously differ.
You u can jump say into pally pvp and easily do very good to start off with, but learn to play some other class properly and the end rewards can be bigger and better.
Maybe look @ sites like
http://www.arenajunkies.com/ &
http://www.sk-gaming.com/arena/ and see what classes are played most?
GL HF